Slip ring unit with debris-collecting means



J. 5. LORD 3,226,666

SLIP RING UNIT WITH DEBRIS-COLLECTING MEANS Dec. 28, 1965 Filed Oct. 8, 1962 FIGZ.

FIGS.

FIGS.

FIG.5.

INVENTOR JOSEPH $.LORD

HIS ATTORNEYS United States Patent T This invention relates generally to slip ring units and,

more particularly, to improvements made in such units to the end of reducing electrical noise and rate of wear.

In a slip ring assembly or unit a transfer of current is effected between a slip ring and a brush which bears on that ring. In the normal operation of the unit, the constant rubbing of the brush surface on the Slip ring surface causes a wearing away of one or both of those surfaces and, consequently, the creation of wear products such as metallic oxide particles and metal fragments. Apart from this wearing effect, in certain applications of the unit the surfaces of the brush and the slip ring become contaminated by foreign matter as, say, a deposit of polymer material generated by the catalysis of air-borne organic vapors.

The presence of any foreign substance on the contact surfaces of the brush and slip ring is disadvantageous because such substance tends to degrade or destroy the good electrical contact between the brush and the ring and to produce unwanted electrical noise in the circuit in which the unit is connected. Also, such foreign substance may abrade the slip ring or brush or both and may increase the rate at which those elements are worn away. Particularly offending in this respect are the metallic wear particles which come from wire or other metal type brushes, and which tend to become workhardened by the friction forces responsible in the first instance for the wearing off of those particles from the brush surface or ring surface. The softer water particles from carbonaceous or graphite brushes are less trouble some from the point of view of their abrading effect on the brush and/ or ring.

It is accordingly, an object of this invention to reduce contamination by wear products and other foreign matter of the contact surfaces of brushes and/ or slip rings of slip ring units.

A further object of this invention is to reduce the electrical noise contributed to a circuit by a slip ring unit.

A still further object of this invention is to reduce the wear of the brush and/ or slip ring elements of slip ring units so as, thereby, to increase the useful life of such units.

These and other objects are realized according to the invention by providing in a slip ring unit at least one debris-collecting channel or slot formed in a slip ring of the unit (or in a brush contacting that ring) to extend across and be open to the track followed on the surface of the slip ring by the brush. The slot acts as a well or storage space for wear products or other foreign matter contaminating the contact surface of the ring and/ or the contact surface of the brush.

When the ring and the brush undergo relative rotation, the relative motion therebetween effects a dislodgement of such foreign matter from one or both of those surfaces and, thereafter, a sweeping of the dislodged debris into the mentioned slot. In this manner, the contact surfaces of the brush and of the ring are kept clean to maintain good electrical contact between those elements and to minimize the rate at which the brush and ring are Worn down.

The described brush and ring comprise separate parts of a slip ring unit which is of the type normally used in instruments, gyros or similar precision devices. Such in- 3,226,666 Patented Dec. 28, 1965 strument type units dilfer from the brush and slip ring combinations used in power machinery (such as large size motors and generators) in that the discussed switch units are generally required to handle only relatively small values of current and voltage (e.g., on the order of milliamperes for current and millivolts for voltage), and in that those units are generally employed in circuits containing resistance external to the unit which is so large (e.g. on the order of hundreds or thousands of ohms or more) compared to the brush-to-slip ring contact resistance (which may be on the order of from 0.1 to 10 ohm) that the resistance provided in the circuit by that contact resistance is a very small part or negligible part of the entire resistance in the circuit.

While so directed to instrument type slip ring units, the invention is not limited to the use in such units of a slip ring or slot of particular shape or to the use of a particular kind of brush. Thus, the invention embraces slip ring units wherein the slip ring contact surface is, for example, an outer cylindrical surface, an inner cylindrical surface or an annular planar surface, and wherein the debris-collecting slot or slots have a cross section which is, for example, V-shaped, U-shaped, rectangular, partly circular or of some other configuration. Moreover, while the invention is of particular utility in connection with metal type brushes (e.g., wire brushes) because of the serious abrasion caused by wear particles from that type of brush, the invention is also of application when the brush or brushes are of the carbonaceous or graphite type, or are metal-graphite type. While, broadly speaking, the invention is not limited to one debris-collecting slot per brush track, to have only one such slot per brush track is preferred and is an aspect of the present invention. The reasons why only one slot per brush track is preferable will be later explained in detail.

For a better understanding of the invention, reference is made to the following descriptions of exemplary ernbodiments there-of and to the accompanying drawings wherein:

FIGURE 1 is a schematic isometric view of a simple slip ring unit according to the invention;

FIGURES 2 and 3 are schematic isometric views of slip ring units which embody the invention, but which differ in form from each other and from the FIGURE 1 unit;

FIGURE 4 is a schematic end view of a slip ring unit differing from those shown by FIGURES l-3 in that the slip ring of the FIGURE 4 unit is unslotted;

FIGURES 5 and 6 are fragmentary end views of modifications of the shape of the slot or slots used in any one of the units shown by FIGURES 1-4 inclusive;

FIGURE 7 is a schematic isometric view of a slip ring unit embodying the invention and employing a plurality of brushes and a corresponding plurality of slots;

FIGURE 8 is a schematic end view of the FIGURE 7 unit;

FIGURE 9 is a schematic end view of a modification of the FIGURE 7 unit; and

FIGURE 10 is a schematic isometric View of the FIG- URE 7 unit as modified to have a single slot instead of a plurality of slots.

Referring now to FIGURE 1, the drawing shows a slip ring assembly or unit having a cylindrical slip ring 20 which may be a wholly electroconductive member on alternatively, the combination of an inside cylinder of insulating material and an outside peripheral band or coating of electroconductive material. The slip ring 20 is mounted on a shaft 21 to be rotatable in the direction indicated by the arrow 22.

Seated on the cylindrical electroconductive surface 23 of slip ring 20 is the foot 24 of an electroconductive brush 25 also comprised of a resilient arm 26 by which the 7 slot.

brush foot is carried at one end of the arm. .The other end of arm 26 is connected t a support (not shown) in such manner that the resilience of the arm maintains the brush foot 24 in pressure contact with the surface 23 of the slip ring.

The rotation of ring produces between that ring and brush 25 a relative rotary motion causing the brush foot '24to move over the slip ring surface 23 in a circular track indicated by the dotted lines 30. As the brush so moves, current transfer takes place between the brush and the slip ring through the areal zone over which the undersurface 31 of the brush (only one edge of surface 31 .being shown) is in contact with the portion 32 of slip ring surface 23 which lies within the dotted lines 30, and which is, accordingly, the electroconductive surface of slip ring 20 over which the brush track extends. The surface 31 of the brush and the surface 32 of the ring are referred to herein as, respectively, the brush contact surface and the ring contact surface. I

, The ring 20 has formed therein a rectangular channel or slot 35 produced by broaching (or by some other suitable machining or forming operation) and extending between the opposite ends of the ring and across the track followed over the surface of the ring by the brush foot 24. In the FIGURE 1 unit, the channel passes through ring 20 beneath track 30 and is open to the track by way of the slot opening of the channel. As shown, the sidewalls 36 and- 37 of slot 35 intersect with the con- .tact surface 32 f the ring'to form conjointly therewith the sharp edges 38 and 39 disposed at'the outward termination "of the slot; As-the-ring rotates in the direction shown by arrow 22, the brush foot 24 passes first over the edge 33 and then over the edge 39. Thus, those edges 38 and 39 are, respectively, the leading and trailing edges of the slot opening for that particular direction of brush motion. The width of slot 35 as measured in the course of track 30 and between the edges 38 and 39 is about two-thirds of the length of the brush foot 24 in the course of the track 30.

As also shown, the slot 35 has left-hand and right-hand open ends and 46 which have a small angular displace ment from each other around the periphery of the ring 20. Because of this angular displacement, the center line of slot 35 is somewhat skewed in relation to the axis of ring 20. As a result, the slot 35 as it extends across track 30 is not exactly normal to the course of that track in the vicinity of such slot, but, instead, is slightly skewed in relation to that course.

As the slip ring 20 undergoes a revolution in the direction shown, foreign matter on the contact surface 32 of the ring is dislodged from its resting place and is swept by the brush foot 24 into the slot 35 as the brush foot approaches and passes over the leading edge 38 of the The debris which is so collected by slot 35 is initially retained in the slot by molecular adhesion or cohesion forces. If, however, an excessive quantity of debris accumulates, the debris is free to dischargefrom slot 35 through the open ends 45 and 46 of the slot. Once the brush foot 24 has crossed in a revolution of ring 2%) from the leading slot edge 38 to the trailing slot edge 39, the sharp slot edge 39 provides a scouring action on the undersurface 31 of the brush to dislodge wear products or other particle debris which may be clinging to that contact surface. Such scoured debris is diverted by edge 39 into the slot 35 to be stored thereby along with the debris previously swept into the slot by the front end of the brush foot. If the direction of rotation of slip ring 20 is reversed from that shown by arrow 22, the described scouring action is provided by the slot edge 38 rather than by the slot edge 39.

The scouring of the brush unde'rsurface by theslot edge is aided by the skewing of the slot 35 relative to the course taken by the brush in following track 30. Another advantage of so skewing the slot relative to the brush track is that such skewing encourages and facilitates the discharge of excess debris collected in the slot from the open end thereof which is lagging relative to the direction of rotation of the slip ring.

In a five hundred hour test conducted at 56 r.p.s. on a slip ring unit similar 'to the one just described, it was found that the debris collecting action'of the slip ring slot eliminated from the contact surface of the ring practically all of the powder which is caused by the wearing of the brush, and which, absent such slot, would have accumulated on that surface to a noticeable degree. At the end of the test, the brush contact surface (a platinumiridium surface) was smooth without grooves, and, moreover, the contact surface of the slip ring (a rhodium surface) was clean and relatively unworn. Another significant and somewhat surprising phenomenon observed during the test was the variation with time of the electrical noise at the brush-slip ring contact. During the test, the level of that noise continually and steadily decreased from a starting value of 50 millivolts (5 ohms) plus leading and trailing edge bounce to five to ten millivolts (0.5 to 1.0 ohm) at the end of the test.

The passage of a brush over a debris-collecting slot creates an impulse type of electrical noise referred to herein as -bounce." Such bounce is caused primarily by mechanical vibrations which are induced in the brush by its passage over the leading and trailing edges of the slot. Those vibrations produce high frequency variations in the contact pressure between the brush and the slip ring and, consequently, high frequency variations in the contact resistance between those elements. In order to minimize the high frequency noise components arising from bounce, I have found it desirable to incorporate in slip ring units the feature of using only one debris-collecting slot per brush track to thereby limit the bounce noise to only one leading edge bounce and one trailing edge bounce per one revolution of the slip ring relative to the brush. Of course, however, more than one debris-collecting slot per brush track can be used in the event that minimization of bounce noise is not a primary objective.

The use in a slip ring unit of only one debris-collecting slot per brush track has the further advantages of simplifying and cheapening the manufacture of the unit.

It might seem that the use of only one debris-collecting slot per brush track would unduly limit the space available for collection of wear product debris and other debris. I have found, however, that one such slot can be made wide enough to provide by itself all of the debris storage space which is necessary. To the end of furnishing such space, the slot width in the course of track 30 may, for example, be from about one third to about two thirds of the length in the course of that track of the contact surface 31 of the brush foot 24. Preferably, but not necessarily, the slot width should be at least one third of that of the brush foot length because a slot width which is a lesser fraction of brush foot length does not make use to best advantage of the slot as a storage site for debris. Moreover, with the type of brush shown in FIG- URE 1, it is preferable that the slot width not exceed about two thirds of the brush foot length because a slot width which is a greater fraction of that length may tend to increase the electrical noise created by leading edge and trailing edge bounce.

Referring now to FIGURE 2, the slip ring of that figure differs from the FIGURE 1 unit in that in the FIGURE 2 unit the slip ring 50 is a hollow cylinder, the contact surface 51 of the slip ring is on the inside of cylinder 56, such surface is contacted by two wire-type brushes 52a, 5212 on a rotatable shaft 53, and relative movement is produced between the surface 51 and the brushes 52a, 52b by rotating the shaft and brushes. The debris-collecting slot 54- of the FIGURE 2 unit is formed In the slip ring thereof and is otherwise similar to the. debris-collecting slot 35 of the FIGURE 1 unit. Because each brush of the FIGURE 2 unit makes contact in its track with surface 51 over an extent in the course of the track which comes close to being a point, in the FIGURE 2 unit the width of the slot 54 in the course of each brush track is evidently much larger than the mentioned extents in those tracks of the brushes.

The slip ring unit of FIGURE 3 differs from that of FIGURE 2 in that in the FIGURE 3 unit the slip ring 60 is an annular electrocconductive ring mounted in or on an insulating base 61 in the form of a plate, the contact surface 62 of the ring 60 is a flat annular surface, and the two wire type brushes 63a, 63b which contact that surface are carried by an arm 64 adapted, during operation of the FIGURE 3 unit, to move in constant radial alignment around the axis of ring 60 at a fixed distance therefrom. The slip ring 60 has formed therein a debris-collecting slot 65 generally similar to the slot 54 of the FIGURE 2 unit. A difference between the two slots is that the slot 54 of FIGURE 2 is in skewed relation to the courses in its vicinity of the tracks over surface 51 followed by the brushes 52a, 52b. In contrast, the slot 65 of the FIGURE 3 unit is normal to the courses in the vicinity thereof of the track-s followed over ring surface 62 by the brushes 63a, 63b. Accordingly, slot 65 is in unskewed re ation to the brush track courses in its vicinity.

FIGURE 4 shows a slip ring unit which differs from the ones respectively shown by FIGS. l-3, inclusive, in that the FIGURE 4 unit has a cylindrical Slip ring 70 which is unslotted. The outside cylindrical surface 71 of ring 70 provides the electroconductive contact surface therefor. That surface -71 is contacted by the forward ends of a pair of straight metal brushes 72a, 72b pivotably carried at their rear ends by respective brush supports 73a, 73b, the brushes being maintained in pressure contact with surface 71 by conventional means such as springs (not shown). While the brushes 72a, 72b are angularly spaced by 180 around slip ring '70, the two brushes have the same axial position on the surface of that ring.

Relative movement is produced between the ring surface 71 and the brushes 72a, 72b by rotation of a shaft 75 on which the ring 70 is mounted to rotate with the shaft. When such relative movement takes place, the comm-on axial position of the brushes causes both of brushes 72a, 72b to follow the same track over the contact surface 71 of the slip ring.

Debris collection is accomplished in the FIGURE 4 unit by sharp edged slot-s 76a, 76b formed in the forward ends of, respectively, brushes 72a and 72b in such manner that each slot extends across and is open to the track commonly followed over the ring surface '71 by the two brushes. As in the case of the slots of the FIGURE 1 and FIGURE 2 units, each of the slots of the FIGURE 4 unit may be skewed in relation to the course in its vicinity of the brush .track on ring surface 71. To assure that debris initially collected by the slots 76a, 7612 will be trapped in those slots, each of such slots may have on the inside thereof a coating 77 of tacky material (e.g., tar) which adheringly retains debris swept into the slot. A particular advantage of the FIGURE 4 configuration is that, since the debris-collecting slots are formed in the brushes, there is no passage of a brush over a slot, and, accordingly, bounce noise is completely eliminated, and there is no inherent limitation on slot width.

Each of the debris-collecting slots shown in FIGS. 1-4 has a cross section which is rectangular. FIGURE 5 shows a slot or channel 80 of which the cross section has the shape of about A of a circle. A slot of such cross section is advantageous in that such slot provides a greater amount of storage space for a given width of slot opening to the brush track than a slot of rectangular cross section. Another advantage of a slot having a cross section the same as or similar to that shown in FIG. 5 is that the acute angle between the ring surface and the slot wall at the trailing side thereof provides an unusually sharp trailing edge adapted to have an accentuated scouring action on the underside of the brush. -As in the case of the slots shown in FIGURE 4, the slot 80 of FIGURE 5 has on the inside thereof a coating 81 of tacky material slot 110a is different from 6 adapted to adheringly retain debris swept into the slot. The cross section of slot is of a shape which is suitable for the cross-section of any of the debris-collecting slots shown by FIGS. 1-4, inclusive.

FIGURE 6 shows a debris-collecting slot formed in a slip ring and having a V-shaped cross section which is likewise suitable for use as the cross section of any of the debris-collecting slots shown by FIGS. 1-4, inelusive. Because the edges at the slot opening provided by a slot of V cross section are not as angular as the edges of slots of which the cross-section is rectangular (FIGS. 14) or mostly circular (FIGURE 5), the employment of the described V slot is desirable in instances where it is desired to attenuate somewhat the scouring action of the trailing edge of the slot on the underside of the brush.

In lieu of relying entirely on the trailing slot edge to provide the mentioned scouring act-ion, the underside of the brush may be kept clean of debris by the scraping action of a roughened portion of the surface of the slip ring with which thebrush makes contact. Means for scraping the underside of a brush in this wise is shown by FIGURE 6 wherein the slip ring 91 is adapted to Totate in the direction indicated by arrow 92, and wherein the contact surface 93 of the slip ring has formed thereon a roughened portion 94 disposed next to the trailing edge 95 of slot 90 and extending across the track (on surface 93) which is followed by the shown brush 96. As illustrated, the described roughened portion is provided by a series of small saw tooth corrugations 97 formed side by side in the contact surface of the slip ring, each corrugation running parallel to the slot 90. If desired, however, the mentioned roughened portion may be formed in some other suitable manner, as, say, by knurling. Such roughened portion of the contact surface of the slip ring may be advantageously incorporated into the structure of any one of the slip rings shown by FIGS. 1-3, inclusive.

FIGS. 7 and 8 show a slip ring unit which is characterized by many of the features already described and by other features .as well. In the FIGURE 7 unit, the reference numeral 100 designates a cylindrical slip ring having .a peripheral electroconductive surface 101 and adapted to rotate on a shaft 102. The surface 101 is contacted by the underside of each of two axially spaced straight wire brushes 104a, 10% having the same angular position in the direction around ring 190 and electrically connected together in circuit by conductor means (not shown). The rotation of the slip ring causes the brushes 104a, 1041) to move over the surface 101 in separate tracks indicated by, respectively, the dotted lines 105a and the dotted lines 105b. The portions 106a and 106b of surface 101 which are included within, respectively, the dotted lines 105a and the dotted lines 1051) are the contact surfaces of slip ring 100, for respectively, the brush 104a and the brush 10412.

Formed in the left-hand end of slip ring 100 is a rectangular slot a extending in skewed relation across the track 105a for the brush 1164a. A similar slot 1101) is formed in the right-hand end of ring 100 to extend in skewed relation, as shown, across the track 1051; for the brush 10412. The two slots 11th: and lltib are angularly displaced from each other around the ring 100, wherefore the angular spacing at any time of brush 104a from the angular spacing at that time of the brush 10 th from the slot 11%. Because the brushes 104a, 10412 contact their respective track surfaces 106a, 1061) for a brush length in the peripheral direction of ring 1% which comes close to being a point, the width of each of slots litia and 11Gb is substantially greater than that brush length.

As best shown by FIGURE 8, the cross section of ring 109 is made slightly non-circular in a manner which causes the sharp trailing edge 11Sb of slot 11% to be slightly raised relative to the leading edge 11612 of the slot. Such raising of the trailing edge relative to the leading edge 7 provides an improved scouring by the trailing edge of the underside of brush ltidb.

The scouring action of edge 1151') is supplemented by a scouring action of a ronghenedportion 11'7b formed on the surface 1B1 of slip ring 100 to extend next to edge 115b across the track of brush 104k. Such roughened portion may be provided in the manner already described in connection with FIGURE 6.

Debris collected in slot 110!) from the scouring action of the trailing edge 11512 or the roughened portion 117b or from the sweeping action of the brush 10412 is adheringly retained in the slot 11Gb by a coating 118 of tacky material deposited inside the slot on the walls thereof. Such coating 118 is similar to the coatings 7'7 and 81 already discussed in connection with, respectively, FIG- URE 4 and FIGURE 5.

The slot 119a of slip ring 101) is, like slot 110b, characterized (FIGURE 7) by a raised trailing edge 115a, a roughened portion 117a formed on the ring surface 10%) adjacent that edge 115a and, moreover, a coating 118 of tacky material on the inside walls of the slot 110a.

As the FIGURE 7 unit operates, the slots 110a and 11017 thereof collect debris swept and scoured from between the brushes 104a, 104i) and the ring contact surfaces 106a, 10619 in the manner previously described in connection with FIGURE 1. The scouring action of the sharp trailing edges 115a, 11515 of the slots is abetted by the scraping action of the rough portion 117a, 1171) in the manner already discussed in connection with FIGURE 6. While some of the debris collected by slots 110a, 110b may discharge from the open ends of the slots, much of such debris is trapped in the slots by molecular adhesion and cohesion forces and by the adhering action of the coating 118 of tacky material in each of the slots.

Because, as described, the angular spacing at any time of the brush 104a from slot 110a is different from the angular spacing at that time of brush 10% from slot 110b,the brushes 104a and 104b pass at different times over, respectively, the slot 110a and slot 11% to thereby space apart in time the bounce impulse noises arising from the respective slot transits of the two brushes. Thus when brushes 104a, 104b are used redundantly in a common circuit, the level of bounce impulse noise caused in the circuit is much less than what it would be if the two slot crossings by the two brushes of the FIGURE 7 unit were to occur coincidentally. Particularly is this so when the ring rotates at such speed that the bounce imparted to the brush as it makes a slot crossing is suflicient to produce for an instant a complete lifting off or separation of the brush from the ring, i.e. an open circuit between the brush and ring. That transient open brush-ring circuit would introduce a very high level of bounce noise into the circuit in which the slip-ring unit is connected were it not for the fact that during the same instant a closed circuit is still provided through the unit by way of the ring and the other brush.

FIGURE 9' shows a modification of the FIGURE 7 unit in which there is formed in the right hand of ring 100 a second slot 11072 angularly spaced from slot 19Gb. The slot 11077 extends in skewed relation over the track 1435b (FIG. 7) for brush 10 1b and is otherwise similar in extent and shape to slot 11% excepting that the respective raised edges 115b and 115'!) of the slots 110b, 110b are on opposite sides of the slots to which they belong relative to a given direction of rotation of ring 100. By virtue of this opposite disposition of slots 115b and 115'b, the brush 10 b is scoured by a raised trailing slot edge irrespective of the direction of rotation of the slip ring.

While FIGURE 9 shows the right hand end of the FIGURE 7 unit when modified as just described, such modification also includes the forming in the left hand end of slip ring 100 of a second slot (not shown) which is a left hand counterpart of slot 110b and which is related to slot 11011 in the same way as the slot 110b is related to slot 11Gb.

FIGURE 10 shows another modification of the slip ring 10f) of the FIGURE 7 unit. In this latter modification the brushes 104a, 1414b (shown in FIGURE 7 but not in FIGURE 10) move over the exterior surface of a slip ring 103 in brush tracks provided by shallow grooves 120a and 12Gb formed in that surface. Furthermore, the two slip ring slots 110a and 110b, shown in FIGURE 7, have been consolidated in that FIGURE 10 modification into a single groove 121 extending in skewed relation from end to end of the slip ring 100 and across each of the brush tracks 12% and 12%. Because the slot 121 is so skewed while the brushes 104a and 104b have the same angular position, the FIGURE 10 slip ring operates like the FIGURE 7 slip ring to space apart in time the bounce impulse noises which are individually produced by the slot crossings of the two brushes.

The above described embodiments being exemplary only, it will be understood that omissions therefrom, additions thereto and modifications thereof can be made without departing from the invention, and that such invention comprehends embodiments differing in form or detail from these specifically described. Thus, for example, a slot or slots of partly circular cross section as in FIGURE 5 or of V cross section as in FIGURE 6 may be used in place of one, some or all of the slots shown in any of FIGS. 7-10, inclusive. As another example, the features characterizing the FIG. 7 unit of the raised trailing edges for the slots (FIGS. 8 or 9), the tacky coating 118 inside the slots, and the roughened portions next to the slots of the ring surface are features of which one, some or all may be incorporated in the modified slip ring 100' shown in FIGURE 10.

Accordingly, the invention is not to be considered as limited save as is consonant with the wording of the following claims.

I claim:

1. A slip ring unit comprising, a first member in the form of a slip ring, a second member in the form of an electroconductive brush in contact with an electroconductive surface of said ring, said brush and ring being relatively rotatable to produce motion of said brush around a track on said surface, means forming in one of said members a channel open to said track by way of a slot opening extending across said track, said slot opening being bounded on one side thereof by a wall which is provided by the body of said one member and which forms at the outward termination of said opening a sharp edge adapted to scour debris from between said brush and track and to divert said scoured debris into said channel, said edge being raised to form a prominence relative to the outward termination of said slot opening at the side thereof opposite said edge.

2. A slip ring unit comprising, a slip ring, a plurality of brushes disposed in relatively fixed relation in the angular direction around said ring and spaced apart transversely of said direction to each be seated on an electroconductive surface portion of said ring, said ring being rotatable relative to said brushes to produce motion of each brush around a track on the surface portion contacted by said brush, and channel means formed in the body of said ring to provide in said ring inwardly of the track followed by each brush a length of channel open to such track by way of a length of slot opening extending across such track, said brushes and said channel means being relatively angularly disposed to render different fromrbrush to brush the angular spacing of each brush from the slot opening length across the track followed by that brush.

3. A slip ring unit according to claim 2 in which said plurality of brushes are disposed in line transversely of said angular direction to move in separate transversely spaced tracks over said ring, and in which said channel means comprises a slot formed in said ring so asto have said slot and an opening therefor extend across all of said tracks in skewed relation to the courses thereof in the vicinity of said slot opening.

4. A slip ring unit according to claim 2 in which said brushes are spaced apart transversely of said angular direction to move in separate transversely spaced tracks over said ring, and in which said channel means comprises a plurality of slots formed in said ring so as to have each slot and an opening therefor extend across a respective one of said plurality of tracks.

5. A slip ring unit according to claim 2 wherein said slot opening has a dimension in the course of said track at least one-third of the arcuate extent of the contact surface of a brush, and said channel means being adapted to scavenge debris from between said brush and ring by way of said opening.

6. A slip ring unit according to claim 5 wherein there is only one slot opening across each track, such opening being wholly contained within an angular interval equal to a minor fraction of the circumference of said ring.

7. A slip ring unit comprising, a first member in the 'form a slip ring, a second member in the form of an electroconductive brush in contact with an electroconductive surface of said ring, said brush and ring being relatively rotatable to produce motion of said brush around a track on said surface, said track being defined by a shallow groove in the surface of said ring, means forming in one of said members a channel having at least References Cited by the Examiner UNITED STATES PATENTS 1,495,780 5/1924 Eschholz et a1. 310-232 2,473,526 6/1949 Hood et al 339-5 2,874,362 2/ 1959 Blanding 339-5 2,879,490 3/1959 Campbell et al 339-5 2,923,913 2/1960 Kulka 339-198 FOREIGN PATENTS 302,383 12/1917 Germany. 317,424 8/ 1929 Great Britain.

ALBERT H. KAMPE, Primary Examiner.

JOSEPH D. SEERS, Examiner. 

1. A SLIP RING UNIT COMPRISING, A FIRST MEMBER IN THE FORM OF A SLIP RING, A SECOND MEMBER IN THE FORM OF AN ELECTROCONDUCTIVE BRUSH IN CONTACT WITH AN ELECTROCONDUCTIVE SURFACE OF SAID RING, SAID BRUSH AND RING BEING RELATIVELY ROTATABLE TO PRODUCE MOTION OF SAID BRUSH AROUND A TRACK ON SAID SURFACE, MEANS FORMING IN ONE OF SAID MEMBERS A CHANNEL OPEN TO SAID TRACK BY WAY OF A SLOT OPENING EXTENDING ACROSS SAID TRACK, SAID SLOT OPENING BEING BOUNDED ON ONE SIDE THEREOF BY A WALL WHICH IS PROVIDED BY THE BODY OF SAID ONE MEMBER AND WHICH FORMS AT THE OUTWARD TERMINATION OF SAID OPENING A SHARP EDGE ADAPTED TO SCOUR DEBRIS FROM BETWEEN SAID BRUSH AND TRACK AND TO DIVERT SAID SCOURED DEBRIS INTO SAID CHANNEL, SAID EDGE BEING RAISED TO FORM A PROMINENCE RELATIVE TO THE OUTWARD TERMINATION OF SAID SLOT OPENING AT THE SIDE THEREOF OPPOSITE SAID EDGE. 